[0001] The invention relates generally to the field of copy restriction, and in particular
to an apparatus for applying microdots to media to restrict copying of material protected
by copyright by other than the copyright owner.
BACKGROUND OF THE INVENTION
[0002] Copying of documents has been performed since the first recording of information
in document form and is a valuable means of promulgating information. Unauthorized
copying of documents has also been occurring since the storage of information in document
form first began. For much of the history of information documentation, the procedures
used to copy original documents have been sufficiently cumbersome and costly to provide
a significant impediment to unauthorized copying, thus limiting unauthorized copying
to original documents of high value. However, in more recent times the introduction
of new technologies for reproducing original documents has decreased the cost and
inconvenience of copying documents, thus increasing the need for an effective method
of inhibiting unauthorized copying of a broader range of restricted documents.
[0003] The inability of convenient, low-cost copying technologies to copy original documents
containing color or continuous tone pictorial information restricted unauthorized
copying primarily to black-and-white documents containing textual information and
line art. Recently, the introduction of cost effective document scanning and digital
methods of signal processing and document reproduction have extended the ability to
produce low cost copies of documents containing color and high quality pictorial information.
It is now possible to produce essentially indistinguishable copies of any type of
document quickly, conveniently, and cost effectively. Accordingly, the problem of
unauthorized copying of original documents has been extended from simple black-and-white
text to color documents, documents containing pictorial images, and photographic images.
In particular, restricting the unauthorized duplication of photographic images produced
by professional photographers on digital copying devices has recently become of great
interest.
[0004] U.S. Patents 5,193,853 and 5,018,767 by Wicker, disclose methods for restricting
the unauthorized copying of original documents on devices utilizing opto-electronic
scanning by incorporating spatially regular lines into the original document. The
spacing of the lineations incorporated in the original document are carefully selected
to produce Moiré patterns of low spatial frequency in the reproduced document allowing
it to be easily distinguished from the original and degrading the usefulness of the
reproduction. Although the Moiré patterns produced in the reproduced document are
readily apparent to an observer, the required line pattern incorporated in the original
document to produce the Moiré pattern upon copying is also apparent to an observer
under normal conditions of use. Additionally, production of the Moiré pattern in the
reproduced document requires that specific scanning pitches be employed by the copying
device. Accordingly, this method of restricting unauthorized document copying is applicable
only to documents such as currency or identification cards where the required line
pattern can be incorporated without decreasing the usefulness of the document. Application
of this technique to other high quality documents is unacceptable due to the degradation
of quality and usefulness of the original document.
[0005] U.S. Patent 5,444,779 by Daniele, discloses a method of preventing unauthorized copying
by the printing of a two-dimensional encoded symbol in the original document. Upon
scanning of the original document in an initial step of a copying process, the encoded
symbol is detected in the digital representation of the original document and the
copying process is either inhibited or allowed following billing of associated royalty
fees. to EP Patent Application Number 96202539.1, filed September 11, 1996, by Schildkraut
et al., and titled, "Copy Protection System," discloses the incorporation of a symbol
of a defined shape and color into a document followed by detection of the symbol in
a scanned representation of the document produced by the copying device. In both disclosures,
the incorporated symbol is detectable by an observer under normal conditions of use
and readily defeated by cropping the symbol from the original document prior to copying.
In addition, incorporation of the symbol into the document is required in the generation
of the original document leading to undesired inconvenience and additional cost. Accordingly,
these methods of imparting restriction from unauthorized copying are unacceptable.
[0006] U.S. Patent 5,390,003 by Yamaguchi, et al.; U.S. Patent 5,379,093 by Hashimoto, et
al.; and U.S. Patent 5,231,663 by Earl, et al; disclose methods of recognizing a copy
restricted document by the scanning and analysis of some portion of the original document
and comparison of the signal obtained with the signals stored in the copying device.
When the signal of a copy restricted document is recognized, the copying process is
inhibited. This method of restricting from the unauthorized copying of documents is
limited in application because the signals of all documents to be copy restricted
must be stored in or accessible by each copying device of interest. Because the number
of potential documents to be copy restricted is extremely large and always increasing,
it is impractical to maintain an updated signal database in the copying devices of
interest.
[0007] Methods of encrypting a digital signal into a document produced by digital means
have been disclosed. These methods introduce a signal which can be detected in a copying
system utilizing document scanning and signal processing. These methods offer the
advantage of not being detectable by an observer under normal conditions of use, thus
maintaining the usefulness of high quality copy restricted documents. However, implementation
of these methods is dependent on digital production of original documents. Although
increasing, production of high quality documents using digital means is still limited.
Accordingly, this approach is not useful for restricting the unauthorized copying
of high quality documents produced using non-digital production methods.
[0008] U.S. Patent 5,412,718 by Narasimhalu, et al.; discloses the use of a key associated
with the physical properties of the document substrate which is required to decode
the encrypted document. This method of restricting the unauthorized copying of documents
is unacceptable for applications of interest to the present invention because it requires
encryption of the original document rendering it useless prior to decoding.
[0009] EP Patent Application Number 97200201.8, filed January 24, 1997 by John Gasper, et
al., and titled, "Copy Restrictive System", and EP Patent Application Number 97200202.6,
filed January 24, 1997, by John Gasper, et al., and entitled, "Copy Restrictive Documents"
disclose pre-exposing color photographic paper to spots of blue light to produce an
array of yellow microdots after chemical processing and a method of detecting these
microdots during scanning performed by a digital printing device. Color photographic
paper capable of forming yellow microdots after exposure to spots of blue light is
of the color-negative type.
[0010] Finally, EP Patent Application Number 98200990.4, filed March 30, 1998, by John Gasper,
et al. and entitled "Copy Restrictive System for Color-Reversal Documents", EP Patent
Application Number 98200989.2, filed March 30, 1998, by John Gasper, and entitled
"Copy Restrictive Color-Reversal Documents" disclose pre-exposing color-reversal photographic
paper to spots of blue light to produce an array of minus-yellow microdots after chemical
processing and a method of detecting these microdots during scanning performed by
a digital printing device.
[0011] Many of the methods for making documents copy restrictive discussed above are based
on recognition of a universal mark in documents that will prevent copying documents
containing the mark. Once a copy system recognizes the document as containing such
a copyright mark, the system is automatically prevented from copying the document
without a key code. A problem with this type of system is that a universal key code
may be distributed to all professional photographic developers, any one of which could
the make copies of copyrighted photographs with out paying a fee to the copyright
owner. Thus it would be desirable to have a mark and a key code that is specific to
individual copyright owners.
SUMMARY OF THE INVENTION
[0012] An object of the present invention is to provide an apparatus for producing copy
restrictive documents having a unique pattern that prevents copying by individuals
other than the copyright owner.
[0013] Another object is to provide an apparatus to efficiently expose photographic media
to a sparse array of microspots of colored light with precise two-dimensional spacing,
intensity, and size.
[0014] An additional object of the invention is to provide a light source having a narrow
spectral bandwidth.
[0015] Yet another object of the invention is to use multiple, individually addressable
solid state light sources distributed sparsely along a line across a direction of
motion of a media for producing a unique pattern of microdots.
[0016] Still another object of the invention is adjusting the radiant power emitted by individual
light sources so as to provide a constant exposure intensity when additional optical
elements are positioned between the light sources and the photographic media and when
the output of the light sources varies for a fixed input power.
[0017] The present invention is directed to overcoming one or more of the problems set forth
above. Briefly summarized, according to one aspect of the present invention, there
is provided a system for creating copy restrictive media comprising printing a first
pattern of microdots on a first set of documents and printing a second pattern of
microdots on a second set of documents. A first key code is associated with the first
microdot pattern, which allows a copy machine to copy the first set of documents,
and a second key code is associated with the second microdot pattern, which allows
a copy machine to copy the second set of documents.
[0018] According to one embodiment of the present invention a linear array is comprised
of at least two spatially distributed light sources and an aperture mask for forming
two or more microlight sources from the light sources. An optical element focuses
light from the microlight sources onto a media moving relative to the linear array.
An encoder turns the light sources on and off at regular intervals relative to movement
of the media.
[0019] Another feature of the invention is the ability to precisely align and space solid
state light emitters along a line and to synchronize the light pulses to generate
a sparse array of microdots of colored light with a precise spacing in an orthogonal
directions, to enable a software algorithm in an apparatus such as a digital copy
print station to perform a discrete Fourier transform to verify the specific pitch
of the two-dimensional array of microdots subsequently formed in the image created
by the end user of the media after chemical processing of the media.
[0020] These and other aspects, objects, features, and advantages of the present invention
will be more clearly understood and appreciated from a review of the following detailed
description of the preferred embodiments and appended claims, and by reference to
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021]
Fig. 1 is a plan view of an apparatus with a linear array of light emitting diodes
(LED) according to the present invention.
Fig. 2 is a perspective view of lens array and aperture mask for the apparatus shown
in Fig. 1.
Fig. 3 is a perspective view of an alternate embodiment of a lens array for the apparatus
shown in Fig. 1.
Fig. 4 is a plan view of another embodiment of the invention using optical fibers
and a Dammann filter.
Fig. 5 is a plan view of yet another embodiment of the invention using a micro lens
array.
Fig. 6 is a plan view of an alternate embodiment of the invention using a rotating
polygon.
Fig. 7 is a plan view of microdot patterns that produced by the apparatus in Fig.
1.
Figs. 8 is a plan view of microdot patterns that produced by the apparatus in Figs.
1, 4, and 5.
Figs. 9 is a plan view of microdot patterns that produced by the apparatus in Figs.
1, 4, and 5.
DETAILED DESCRIPTION OF THE INVENTION
[0022] Referring to Fig. 1, in its most general implementation, the inventive apparatus
10 to imparts to color photographic media and in particular color photographic paper
a means of copyright protection. Apparatus 10 is comprised of a printhead 12, drum
14, encoder 16, electronic controller 18.
[0023] Printhead 12 is comprised of a linear array of light sources 20, aperture mask 28,
and lens array 32. The linear array of light sources is composed of spaced, light
emitting sources 22 such as inorganic or organic light-emitting diodes (LEDs) or laser
diodes, that emit predominantly blue light in the range of wavelengths from 400 to
500 nanometers. The light emitting sources 22 are mounted on a ceramic or appropriate
heat sink 24 which in turn is mounted on to a rigid metal base mount 26. Each of the
light emitting sources 22 are separated from each adjacent source by at least 0.5
mm and preferably 1 mm. Each light emitting source has a maximum linear dimension
of 0.3 mm, and preferably less than 0.2 mm.
[0024] As shown in more detail in Fig. 2, the light from each light source 22 illuminates
an appropriate aperture 30, in aperture mask 28, placed over each light source 22.
The illuminated aperture is then imaged by a lens array 32 to a light sensitive media
40. In the preferred embodiment, lens array 32 is a gradient-index rod lens array
33 sold under the trademark Selfoc™, made by NSG America. In an alternate embodiment
lens array 32 is a microlens array 35 of the type shown in Fig. 3.
[0025] Each aperture 30 in the aperture mask 28 is used to restrict the area of the emitted
light that is being imaged onto the light sensitive media 40 so as to form a microspot
34 of focused light of a desired size on the media 40. Each aperture 30 is separated
from each adjacent aperture by at least 0.5 mm and preferably 1 mm. Each aperture
has a maximum linear dimension of 0.2 mm, and preferably less than 0.1 mm. A center
of each aperture in the aperture mask is aligned coaxially with a center of each light
source. After chemical processing of the exposed media, a colored microdot is formed
in the color photographic media.
[0026] Aperture mask 28 is separated from the linear array of light sources 20 by a gap
46 shown in Fig. 1-3. In the preferred embodiment gap 46 is at least 0.1 mm. Gap 46
provides a reduction in the angle subtended 48 by the light passing through the aperture,
thereby reducing the working numerical aperture of the imaging optics to provide a
sharper image wit less flare and increased depth-of-focus than would otherwise be
possible.
[0027] Also, the aperture mask may be coated with a filter material 42 that provides spectral
filtration to block unwanted wavelengths of light. Filter material 42 may be placed
anywhere between light sources 22 and the lens array 32. In one embodiment filter
material is a multi-layer, dielectric, interference filter, and is coated on one surface
of aperture mask 28.
[0028] The separation of the light emitting sources 22 , and the concomitant separation
of the apertures 30, determines the spacing between the microspots 34 of blue light
in a transverse direction i.e. across the width of the media 40. To control the precise
placement of microspots 34 in a longitudinal direction, a high resolution encoder
16 is mounted on drum 14. The drum 14 transports media 40. Encoder pulses are counted
by electronic controller 18 to generate electrical timing signals necessary to pulse
the linear array of light sources 20 at a precise pulse duration at precise intervals
of time. For a given radiant power emitted by the light sources 22, the duration of
the pulse (the time that the light source is on) is variable to obtain a desired exposure
on the photographic media. The encoder 16 provides precise timing pulses irrespective
of any media flutter, which enables precise location of the microdots at a desired
pitch in the longitudinal direction. In some embodiments, it is desirable to keep
the pitch of the microspots along the transverse and longitudinal directions the same.
[0029] By controlling the light pulse duration, the radiant power output from the light
emitting sources 22, and the size of the aperture 30, the size and intensity of the
microspot is controlled. The resulting controlled exposure received by the photographic
media results in a two-dimensional array of microspots of desired size and exposure
to the media. After chemical processing of the media there is formed in the media
colored microdots of the desired size, spacing, and optical density.
[0030] One of the important attributes of the present invention is the precise placement
of the microspots of focused light onto the media. After exposure and chemical processing
of silver halide photosensitive media, an image subsequently recorded by an end user
will contain microdots of the same spacing. This photographic print is rendered copy
restrictive. When an unauthorized attempt is made to copy the print using a copy machine,
for example, a digital printing station, a detection means identifies the unique pattern
of microdots and prevents operation of the copy machine.
[0031] An important aspect of this detection means is the performance of a Fourier transform
to identify the spatial frequency or frequencies of the two-dimensional pattern. Without
accurate positioning of the microspots of light onto the media with adequate precision
and repeatability of location, as well as maintaining a constant radiant energy for
all microspots for all exposed media, it would be far more difficult to develop a
robust software algorithm having a high probability of detecting a pattern that identifies
the media as copy restrictive when this pattern is accompanied by a complex scene
imparted to the media by the end user such as a photograph.
[0032] Another important aspect of the present invention is maintaining an equal radiant
energy to the media for all microspots. In the preferred embodiment employing LEDs,
an aperture mask, and a Selfoc™ array, it is necessary to adjust the applied voltage
to each LED in order to obtain an equal energy exposing the media. This is due in
part to variations in the operating characteristics from one LED to another, variation
in the open area of the apertures from one aperture to another, and a variation in
the brightness of the Selfoc™ image when the position of each micro-light source varies
with respect to the spatial arrangement of the gradient-index rod lenses in the Selfoc™
linear array.
[0033] Another important feature of the present invention is the exposure of the media with
a sparse array of microspots covering typically less than 1% of the surface area.
This is necessary to prevent an increase in the minimum optical density of the media.
Therefore, the duty cycle of the light sources, that is, the fraction of the time
the light source is on and exposing the media is very low, typically less than 5%.
This low duty cycle provides extended operating life for the LEDs or laser diodes.
[0034] Fig. 4 shows an alternate embodiment of an apparatus for creating copy restrictive
media comprising a collimated light source 50, focused to a light modulator 54, recollimated
to a light distributor 58, which distributes light to multiple optical fibers 60.
The distal ends of the optical fibers 60 are aligned into a widely spaced linear array
at a common plane. Light from the distal end of each of the optical fibers 60 is focused
by a lens 62. A Dammann filter 64 positioned adjacent to each lens 62 forms at least
two microspots 66 along a line transverse to a direction of travel of the media 40.
Encoder 16 and electronic controller 18 function as described above.
[0035] Fig. 5 shows another embodiment of an apparatus for creating copy restrictive media
comprising a collimated light source 50, focused to a light modulator 54, recollimated
to a light distributor 58, which distributes light to multiple optical fibers 60.
The distal ends of the optical fibers 60 are aligned into a widely spaced linear array
at a common plane. Light from the distal end of each of the optical fibers 60 is focused
by a lens 62 to the media 40 to form a microspot 66 along a line transverse to the
direction of travel of the media 40. Encoder 16 and electronic controller 18 function
as described above.
[0036] Fig. 6 shows yet another embodiment of an apparatus for creating copy restrictive
media comprising a collimated light source 50, focused to a light modulator 54, recollimated
by a lens 56. The collimated beam is scanned across media 40 by rotating polygon 70.
An f-theta lens 74, located between polygon 70 and media 40, focuses the scanning
beam to microspots 66 in a direction transverse to the direction of travel of the
media. Driver 72 rotates polygon 70. Encoder 16 and electronic controller 18 function
as described above.
[0037] Referring to Fig. 7, a series of microdot patterns 80, 82, and 84 are shown produced
by an LED apparatus such as shown in Fig. 1. Each of the specific patterns are produced
by writing a unique sequence of pulses from selected LEDs. The microdot pattern 80
was formed by turning off LEDs at columns 2, 6, and 10; in line 3 and line 5. This
microdot pattern would then be repeated after line 8. The microdot pattern produced
in 82 is achieved by not exposing columns 2, 6 and 10. The microdot pattern in 84
is produced by turning off LEDs in a staggered sequence, for example column 3in line
3, column 4 in line 4, etc. Each of these unique microdot patterns would be placed
on photograph paper sold to a particular customer, and only that customer would be
given the key code to unlock copy machines to copy a photograph produced on that paper.
[0038] Referring to Fig. 8, another series of microdot patterns 86, 88, and 90 are shown.
These microdot patterns are produced by a collimated light source, such as the apparatus
shown in Figs. 4-6 and show some of the microdot patterns that may be produced by
writing a unique sequence of pulses from the modulated light source. The arrows show
the direction of travel of the media. The microdot pattern in 86 has every fourth
row deleted, the pattern in 88 has every other row deleted, and the pattern in 90
has every seventh row deleted.
[0039] In a similar manner, Fig. 9 show additional microdot patterns. Microdot pattern 92
has alternate microdots in odd number rows and no microdots in even numbered rows.
Microdot pattern 94 is a hexagonal pattern. Microdot pattern 96 has regularly spaced
microdots in odd numbered rows and a two on, two off spacing in even numbered rows.
Microdot pattern 98 has regularly spaced microdots in odd numbered rows and a one
on, one off spacing in even numbered rows.
[0040] In the preferred embodiment of the invention, the microdot pattern is formed to produce
a Fourier transform when scanned. This makes detection of the microdot pattern by
a software algorithm easier than using other systems. A unique key code to unlock
copy machines is assigned to customers. Thus customers using photographic paper with
a microdot pattern matching the key code will be able to copy photographs made on
that paper, but other individuals will not be able to make copies.
1. A system for creating copy restrictive documents
comprising: printing a first pattern of microdots on a first set of documents; and
printing a second pattern of microdots on a second set of documents.
2. A system as in claim 1 wherein a first key code is associated with said first microdot
pattern wherein said first key code unlocks a copy machine to allow reproduction of
said first set of documents.
3. A system as in claim 2 wherein said first key code is a Fourier transform of said
first microdot pattern.
4. A system as in claim 1 wherein said first pattern of microdots is produced by omitting
alternate rows of microdots.
5. A system as in claim 1 wherein said first pattern of microdots is produced by omitting
alternate columns of microdots.
6. A system as in claim 1 wherein said first pattern of microdots is produced by omitting
alternate columns of microdots and alternate rows of microdots.
7. A system as in claim 1 wherein a second key code is associated with said second microdot
pattern wherein said second key code unlocks a copy machine to allow reproduction
of said second set of documents.
8. A method for producing copy restrictive documents comprising the steps of:
printing a first pattern of microdots on a first set of documents;
printing a second pattern of microdots on a second set of documents;
generating a first key code associated with said first microdot pattern wherein said
first key code unlocks a copy machine to allow reproduction of said first set of documents;
and
generating a second key code associated with said second microdot pattern wherein
said second key code unlocks a copy machine to allow reproduction of said second set
of documents.
9. A method as in claim 8 wherein a first customer is assigned said first key code.
10. A method as in claim 8 wherein a second customer is assigned said second key code.
11. An apparatus for creating copy restrictive media comprising:
a linear array comprised of at least two spatially distributed light sources;
an aperture mask for forming two or more micro-light sources from said light sources;
an optical element for focusing light from said micro-light sources onto a media moving
transverse to said linear array; and
an encoder for turning said light sources on and off at regular intervals relating
to movement of said media.